1. Field of the Invention
The present invention relates to an information recording medium for recording video information, audio information or the like, a method for reproducing information recorded in the information recording medium, and an apparatus for reproducing information recorded in the information recording medium. In particular, the present invention relates to an information recording medium in which copyrighted content information is recorded, a method for reproducing copyrighted content information recorded in the information recording medium, and an apparatus for reproducing copyrighted content information recorded in the information recording medium.
2. Description of the Related Art
Recently, recording mediums, each for recording an analog signal, such as a compact cassette tape, an analog record and the like, have been replaced as the mainstream of recording mediums for audio information by a recording medium for recording a digital signal, such as a CD (Compact Disc), a MD (Mini Disc) and the like. Moreover, the digital recording mediums, such as a video CD for recording a video signal compressed by a compression method called MPEG1 on a CD, and a DVD (Digital Video Disc) for recording a video signal compressed by a high-quality compression method called MPEG2 on an optical disk having a large capacity of 4.7 GB, have been developed as recording mediums for recording a video signal. These digital recording mediums have been commercialized as recording mediums for recording video information and audio information.
FIG. 7 is a block diagram showing an internal configuration of an optical disk reproducing apparatus 400 of a first prior art. The optical disk reproducing apparatus 400 executes error correction and expansion processes on information data read out from an optical disk 201, thereby decoding and outputting desired video and audio signals.
Referring to FIG. 7, the optical disk reproducing apparatus 400 is equipped with the optical disk 201. The optical disk reproducing apparatus 400 is constituted by a spindle motor 202, an optical head 203, a head amplifier 204, an analog processor 205, an optical disk controller 206, an error correction memory 207, an audio and video decoder 209 (hereinafter referred to as an AV decoder), an audio and video signal processing memory 210 (hereinafter referred to as an AV signal processing memory), a servo controller 211, a CPU 212, and a CPU bus 213.
The spindle motor 202 rotates the optical disk 201 in accordance with a control signal from the servo controller 211. The optical head 203 comprises an optical pickup. The optical head 203 irradiates the optical disk 201 with laser light generated by driving a laser diode. The optical head 203 detects the reflected light from the optical disk 201, and then, executes photoelectric conversion on the reflected light. Then, the optical head 203 outputs a reproduced signal subjected to photoelectric conversion to the analog processor 205 through the head amplifier 204. The analog processor 205 has facilities for AGC, equalizing, data slice, and PLL. The analog processor 205 applies predetermined analog signal processing to the input reproduced signal, and then outputs the processed reproduced signal to the optical disk controller 206. Subsequently, the optical disk controller 206 converts the input reproduced signal into reproduced digital data through A/D conversion, and then demodulates the reproduced data. The optical disk controller 206 applies error correction and the like to the demodulated reproduced data by using the error correction memory 207 as a buffer memory.
Then, the optical disk controller 206 outputs the processed reproduced data to the AV decoder 209. Furthermore, the AV decoder 209 applies decoding including expansion to video data and audio data, which are compressed into the above-mentioned input reproduced data, by using the AV signal processing memory 210 that is an expansion buffer memory for use in expansion of video data and audio data, in accordance with the input reproduced data. Then, the AV decoder 209 outputs the processed video and audio signals.
The servo controller 211 controls the spindle motor 202, the optical head 203, the optical disk controller 206 and so on in accordance with the signals from the analog processor 205, the optical disk controller 206 and the CPU 212, to perform servo control of focusing, tracking or the like of the optical head 203 for readout of data from the optical disk 201, or the like. The servo controller 211, the analog processor 205, the optical disk controller 206 and the AV decoder 209 are connected to the CPU 212 through the CPU bus 213. The CPU 212 controls the analog processor 205, the optical disk controller 206, the AV decoder 209 and the servo controller 211 through the CPU bus 213, to control operation of the overall optical disk reproducing apparatus 400.
An operation of the optical disk reproducing apparatus of the first prior art will be briefly described with reference to FIG. 7. The CPU 212 controls the optical head 203 in accordance with a predetermined sequence so as to read out data from the optical disk 201 by using the optical head 203, then output the reproduced data to the optical disk controller 206 through the head amplifier 204 and the analog processor 205, and then store the reproduced data subjected to error correction in the error correction memory 207. At that time, the CPU 212 reads out control information and data identification information in the reproduced data stored in the error correction memory 207, and thus controls the servo controller 211 and the AV decoder 209, thereby reproducing video data and audio data.
On the other hand, the capacity of an application program for a personal computer has also increased in accordance with an improvement in performance of the personal computer and an increase in the capacity of a hard disk. A DVD is used, by making use of its large capacity, not only as a recording medium for recording video data and audio data, but also as a medium for distributing application software for the personal computer, or the like. Thus, a DVD drive unit is rapidly spreading as a peripheral unit of the personal computer. Furthermore, an AV decoder card having an MPEG expansion facility for the personal computer, a program for executing the MPEG expansion facility through software processing by a main processor of the personal computer and the like have been commercialized.
However, the DVD drive unit and the AV decoder card are connected through a communication line of a general computer bus in a system in which the personal computer reproduces video data and audio data from the DVD by using the DVD drive unit and the AV decoder card. Thus, acts, such as piracy of data transmitted through the communication line and distribution of tampered data, take place. Consequently, there is such a problem in that it is very difficult to protect the copyright thereof.
In order to solve the above-mentioned problems, encryption and recording of copyrighted data have been proposed in Japanese patent laid-open publication No. 7-249264 (hereinafter referred to as a second prior art), for example. Proposed is a method in which a cipher key is recorded in a main data area of a different sector from an encrypted data sector in a CD-ROM of the second prior art. In the second prior art, data encrypted at the time of recording and a cipher key of the data are recorded in the CD-ROM. At the time of reproducing, a personal computer issues a command to read a cipher key to a reproducing apparatus, then encrypted data is read out, and the encrypted data is decrypted by using the cipher key previously read out, and this leads to the data being reproduced.
However, in the second prior art, the cipher key is recorded in the main data area of the sector from which the cipher key can be read out by a general read command. Thus, the cipher key can be easily read out by a general personal computer. Therefore, a user can read out the cipher key and encrypted data. Thus, the second prior art has a problem in that it involves a high risk of decryption. The second prior art has another problem that a pirated copy can be made by copying the cipher key and the encrypted data in a hard disk memory, for example.
Moreover, all the main data areas of the sector are encrypted and recorded. Thus, when a CPU of, for example, a DVD player attempts to read out content control information, which is included in main data of the sector and includes content identification information, content copy control information and so on, from an optical disk in order to control the DVD player, the CPU can obtain correct information only after decrypting data once encrypted.
The above-mentioned problem causes the following problem. When the area containing the content control information is recorded in a form of plain text, unauthorized reproducing takes place in the case where the copy control information is tampered with.